Wear and tool life of CBN cutting tools

The wide application of precise high-quality components made of advanced structural materials is directly related to the accelerating use of superhard materials and tools made of them. When machining with these tools, the optimal choice of cutting process parameters is important, as the requirements concerning the parts can often only be satisfied by cutting under extreme conditions (small chip cross-section, high cutting speed, special materials, new wear forms, etc.). Polycrystalline CBN tools are widely used for the fine turning of parts made of construction, stainless, heat-resistant, acid-resistant or even hardened (60-70 HRC) HS steels. The experimental T = T(v(c)) tool life curves are of "dromedary" type. The tool life maximum point moves up and down according to changes of depth of cut and feed-rate values. The reasons for polyextreme tool life curves and moving maximum tool-life points are discussed in the paper. A new general tool life Eq. is outlined which reflects the physical principles of cutting phenomena more completely and exactly. The suggested form describes the polyextreme structure of the tool life function, while the position of the extreme values (along the T- and v(c)-axis) depend on the cutting parameters.